The rolling bearings are generally classified into ball bearings and roller bearings according to the kind of rolling members, and each group can be further classified.
Among known holders for ball bearings there are an ordinary holder shown in FIG. 1, a crown holder shown in FIG. 2, a holder for an angular bearing shown in FIG. 3, a holder for a thrust bearing (not shown) etc. Among known holders for roller bearings there are a holder for a conical roller bearing shown in FIG. 4, that for a spherical roller bearing shown in FIG. 5, that for cylindrical roller bearing shown in FIG. 6, that for a thrust bearing (not shown), that for a thrust spherical bearing (not shown) etc.
Plastic holders have heretofore been prepared with so-called engineering plastic material such as polyamide (nylon), polyacetal, polybutylene terephthalate, fluorinated resins etc. singly or in the form of a composite material reinforced with short fibers such as glass fibers or carbon fibers. Among these materials, the polyamide resin has been widely employed for the plastic holders because of satisfactory balance of the material cost and the performance, and excellent characteristics have been confirmed under medium work conditions. However, this material shows deterioration over a long period and cannot meet the market requirements under a condition of continuous use at a temperature exceeding 120.degree. C., or under a condition of continuous or intermittent contact with oils added with extreme pressure agents, oils or chemicals such as acids.
For plastic holders for bearings to be used under a high temperature condition exceeding 150.degree. C., there have been proposed so-called super engineering plastics such as polyethersulfone (PES), polyetherimide (PEI), polyamide-imide (PAI) or polyether-etherketone (PEEK) as reported for example in the Ball Bearing Journal, 227, 14, 1986. However, these materials have not been employed widely because they are very expensive and are still inadequate as to physical properties required for the holders such as suitable flexibility required at the molding or assembling and fatigue resistance, though they are excellent in resistances to heat and chemicals.
Polyphenylene sulfide (PPS) is relatively inexpensive and is known to be usable for the plastic holder for use under a high temperature, but it is very brittle and insufficient in mechanical properties for use in the holders. The PPS resin is known as a crystalline thermoplastic resin consisting of alternate bonding of benzene rings and sulfur atoms. In the conventional PPS resins, crosslinked or branched structures are partially introduced by a heat treatment under a high temperature or by intentional addition of a crosslinking agent or a branching agent in the course of manufacture (hereinafter called branched PPS resins). The conventional PPS resins of a high molecular weight, being generally obtained by heating PPS of relatively low molecular weight for 1-24 hours at a high temperature in air or in an oxygen-containing gas, have branched chains or crosslinked portions due to a crosslinking reaction of active terminal groups. Also the Japanese Laid-open Patent 53-136100 disclosed a method of obtaining branched PPS resins, employing a trivalent or higher-valent polyhalogenated aromatic compound as a cross-linking or branching agent. A representative example of commercial branched PPS resins is Ryton (trade name) supplied by Philips Petroleum Inc., U.S.A.
On the other hand, there are recently developed PPS resins in which the molecular chain is linearly grown to a high molecular weight in the course of polymerization (hereinafter called linear-chain PPS resins), as disclosed in the Japanese Laid-open Patents 61-7332 and 61-66720. Such linear-chain PPS resins are characterized by a tenacity which is higher than that of the branched PPS resins, since the molecular chains of the linear-chain PPS are substantially free from branched chains and can more easily entangle mutually.
For conventional molding, branched PPS resins containing branched portions or partially crosslinked portions have been principally employed. In comparison with the linear-chain PPS resins, the branched PPS resins are more brittle because of the lower tenacity. Thus, the molding form has to be limited to a certain range for the holders requiring considerably forced demolding operations thereof after molding, such as a holder for crown ball bearing, that for conical roller bearing, or that for spherical or cylindrical roller bearing with a high coverage on rollers. Also, the holders composed of the branched PPS resin are apt to show breakage of claws, pillars, rings or flanges of the holder at the assembly of the bearing. These drawbacks are all derived from the inherent lack of flexibility of the branched PPS resins, and are the principal reason why the PPS resins are not commercially employed in the manufacture of bearing holders.